The invention relates to a process for the preparation of xcex1-olefin polymers, especially polypropene, having a controlled stereoregularity, comprising the successive steps of: (i) producing a first polymerization product by contacting under polymerization conditions an xcex1-olefin monomer with a polymerization catalyst system comprising a transition metal compound, a first organometal compound and a stereoregulating external electron donor, to give a first polymerization reaction mixture; (ii) producing a second polymerization product by contacting an xcex1-olefin monomer with at least the first polymerization reaction mixture.
The word xe2x80x9ccomprisingxe2x80x9d means that the subsequently listed subject matter must be included, but that further subject matter may also be included. It is open. See Grubb, P. W., Patents in Chemistry and Biotechnology, Clarendon Press, Oxford, 1986, p. 220.
The first and second polymerization products may have the same or different melt flow rate (MFR) values. The MFR values disclosed here are measured according to the standard ISO 1133 at 230xc2x0 C. using a 2.16 kg load.
By xcex1-olefin monomer is in this connection meant an xcex1-olefin which is capable of polymerization by the insertion (Ziegler-Natta) mechanism. An xcex1-olefin is a compound having the structure CH2xe2x95x90CHR, wherein R is a linear or cyclic alkyl group. Typical xcex1-olefin monomers of the invention are propene (R=xe2x80x94CH3), butene-1 (R=xe2x80x94CH2CH3), 4-methylpentene-1 (R=CH2CH(CH3)2), hexene-1 (R=xe2x80x94(CH2)3CH3) and octene-1 (R=xe2x80x94(CH2)5CH3). By an xcex1-olefin polymer is meant an xcex1-olefin homopolymer or copolymer. As monomers to be copolymerized can, in addition to xcex1-olefin monomers of the above mentioned type, also be used ethene. By transition metal compound is in this connection meant a transition metal compound which is capable of contributing to the polymerization ability of said polymerization catalyst system. The transition metal compound is the basis of the Ziegler-Natta system""s so called xe2x80x9ccatalystxe2x80x9d or xe2x80x9cprocatalystxe2x80x9d. By first organometal compound is in this connection meant an organometal compound which is capable of contributing to the polymerization ability of said polymerization catalyst system. The organometal compound is also called the xe2x80x9ccocatalystxe2x80x9d of the Ziegler-Natta system.
The presence of a stereoregulating electron donor in an xcex1-olefin polymerization catalyst produces a stereospecific polymer. Such a polymer usually has high isotacticity, i.e. a high portion of xcex1-olefin mers in the macromolecular chain having the same configuration with respect to a common direction along the chain. With propene polymers, the isotactic index I.I., measured as the percentage of a polypropene sample which is insoluble in boiling n-hexane, or the xylene soluble fraction XS thereof, is a measure of the isotacticity of the polymer. Isotactic macromolecules are associated and crystallized whereby their solubility is lower. Thus, the lower the XS of an xcex1-olefin polymer, the higher is its isotacticity. The isotacticity may also be measured by Fourier Transform Infrared Spectroscopy (FTIR).
The preparation of highly stereoregular polymers of C3-C10-xcex1-olefins, such as propene, in many phases or steps, is known e.g. from JP Patent Application 91048, EP Patent Specification 339 804 and FI Patent Application 961722.
According to the examples of the last mentioned document, propylene is in a first step polymerized in the presence of an MgCl2/TiCl4/Et3Al/D (D=stereoregulating external electron donor, Et=ethyl) type catalyst system and no or little hydrogen as molar mass limiting termination agent into a stereoregular propylene polymer having a low MFR, and in a second step polymerized in the presence of the same catalyst system and a large amount of hydrogen termination agent into a stereoregular propylene polymer having a high MFR. The result is a stereoregular propene polymer product having a broad molar mass distribution in the form of a low MFR (high molar mass) fraction and a high MFR (low molar mass) fraction.
It is assumed that the overall high stereoregularity and the presence of a polymer fraction of low MFR gives good strength and rigidity as well as low creep to the polymer product. The presence of a polymer fraction of high MFR, on the other hand, gives good melt processability and flexibility to the polymer product.
In multi-phase or -stage processes of the above mentioned type for the preparation of xcex1-olefin polymers, the isotacticities tend to vary between the phases or stages of the process, due to different conditions and donor concentrations, and control of the isotacticity is sometimes difficult. For example, if the average XS of the product in the preceding step is 3-3.5%, in the subsequent step it might have decreased to only 2-2.5%. In practice, this means that the polymer fraction produced in the subsequent step or steps has an XS of below 1.5%. In some applications such as in film and fibre products the isotacticity of the propene polymer needs to be controlled to give an XS value of about 3.5-4%. In order to reach such XS values for the final product in an uncontrolled propene polymerization process, the XS in the first reactor should be more than 5%, because the second reactor is producing an XS of only 2-3%. However, this kind of isotacticity and crystallinity difference between the materials of the first and second steps results in homogeneity problems which can be detrimental for the film and fibre products.
The above mentioned problems and findings relating to the multi-stage production of xcex1-olefin polymer products have now been dealt with principally in the following way.
As was previously mentioned, the present invention relates to a process for the polymerization of an xcex1-olefin polymer having controlled stereoregularity. In the process, a first and a second polymerization product are produced by contacting an xcex1-olefin with a high activity polymerization catalyst system comprising a first organometal compound in two steps (i) and (ii).
Now, it has been realized that the above mentioned problem can be solved, if in the process, the second polymerization product is produced in the presence of a stereoregularity controlling agent in step (ii). The stereoregularity controlling agent is selected from a second organometal compound which contains, on an atom basis, more halogen per metal than the first organometal compound, or 0.01-1.2% of an olefin which is not said used xcex1-olefin monomer(s), calculated on the total molar amount of the olefin and the xcex1-olefin monomer(s).
It has also been found that in view of the quality of some end products, more important than the level of XS of the polymer obtained from the reactor system is that the XS values are essentially on the same level in every phase or stage of the process. Especially very good quality fibres and films, but also different molding applications are achieved with polymers, which are produced in multi-phase or -stage process where isotacticities, i.e. XS values, are controlled to essentially the same level in every phase or stage.
According to a preferred embodiment of the present invention, controlling the stereoregularity means especially controlling the stereoregularity to essentially the same level in every phase or stage of the process, i.e. the isotacticities or XS values are balanced in every phase or stage of the process.
The improvements obtained by using a more halogenated organometal compound and/or small amounts of olefins when producing the second polymer fraction are verified by the examples.
The polymer products prepared according to the process of the invention may be unimodal polymers or bimodal polymers with narrow or more or less broad molecular mass distribution. MFR values can vary in wide ranges from 0.03 to 2000 g/10 min. Unimodal polymers, i.e. polymers having the same MFR values in every phase are especially suitable e.g. for fibre applications.
The xcex1-olefin monomer has been defined above. Preferably, it is a C3-C8-xcex1-olefin. The most preferred xcex1-olefin monomer is propene. In either or both of steps (i) and (ii), one or more comonomers may be used. They may be xcex1-olefin monomers as defined above. However, ethene is the most advantageous comonomer, when a comonomer is used. In step (ii) the amount of comonomer is preferably less than 10%, based on the total amount of monomers.
According to an embodiment of the invention, the first organometallic compound is a conventional so called cocatalyst, preferably a first organoaluminium compound. More preferably, the first organoaluminium compound has the formula (1)
R3mxe2x88x92nAlmXnxe2x80x83xe2x80x83(1)
wherein R is a C1-C12 alkyl, X is a halogen, m is 1 or 2 and n is an integer such that 0xe2x89xa6n less than 3mxe2x88x921. Advantageously, the first organoaluminium compound having the formula (1) is a tri-C1-C12 alkyl aluminium, most preferably triethyl aluminium TEA.
According to an embodiment of the invention, the second organometal compound is a second organoaluminium compound. Typically, it is selected among more halogenated so called olefin polymerization cocatalysts. See above. Preferably, the second organoaluminium compound has the formula (2)
Rxe2x80x23mxe2x80x2xe2x88x92nxe2x80x2Almxe2x80x2Xxe2x80x2nxe2x80x2xe2x80x83xe2x80x83(2)
wherein Rxe2x80x2 is a C1-C12 alkyl, Xxe2x80x2 is a halogen, mxe2x80x2 is 1 or 2 and nxe2x80x2 is such an integer that nxe2x80x2/mxe2x80x2 greater than n/m, wherein n and m are the same as in formula (1), and nxe2x80x2 less than 3mxe2x80x2. Advantageously, the second organoaluminium compound which has the formula (2) is selected from C1-C4 alkylaluminium dihalides such as ethylaluminium dichloride (EASC), di-C1-C4 alkylaluminium halides such as diethylaluminium chloride (DEAC) and C1-C4 alkylaluminium sesquihalides such as ethylaluminium sesquichloride (EADC), as well as mixtures thereof. The most preferable second organoaluminium compound which has the formula (2) is EADC. DEAC is also preferable, because it contains much less chlorine than e.g. EADC (about half of the chlorine amount of EADC), and can therefore be used in very wide range of low chlorine applications such as food packages.
It should be born in mind that the above mentioned first and second organometal compounds are not selected independently, but always so that the second organometal compound has more halogen per metal than the first one. Typical first organometal compound/second organometal compound pairs of the invention are trialkyl aluminium/dialkyl aluminium halide, trialkyl aluminium/alkyl aluminium sesquihalide, trialkyl aluminium/alkyl aluminium dihalide, dialkyl aluminium halide/alkyl aluminium sesquihalide, dialkyl aluminium halide/alkyl aluminium dihalide, alkyl aluminium sesquihalide/alkyl aluminium dihalide. Preferable first organometal compound/second organometal compound pairs of the invention are triethyl aluminium/diethyl aluminium chloride, triethyl aluminium/ethyl aluminium sesquichloride, triethyl aluminium/ethyl aluminium dichloride, diethyl aluminium chloride/ethyl aluminium sesquichloride, diethyl aluminium chloride/ethyl aluminium dichloride and ethyl aluminium sesquichloride/ethyl aluminium dichloride. The most preferable first organometal compound/second organometal compound pair is triethyl aluminium/ethyl aluminium dichloride.
As was said above, the isotacticity can be controlled by using a halogen containing organometal compound when preparing the second polymerization product. According to another embodiment of the invention, the isotacticity can be controlled by using a small amount of an olefin other than the xcex1-olefin monomer(s), such as ethene when preparing the second polymerization product. The olefin used in small amounts in step (ii) is selected among olefins (ethene and xcex1-olefins) which are not the same as the xcex1-olefin monomer used in the present invention. The most preferable olefin used in step (ii) in small amounts is ethene. The olefin can be used with or without the halogen containing organometal compound. The amount of olefin is 0.001-1.2%, based on the total molar amount of the olefin and the xcex1-olefin monomer(s). Preferably, it is 0.08-0.8%, most preferably 0.1-0.4%.
The organometal compounds are selected and the small amount of olefin are used according to their assumed ability to interact with the stereoregulating external electron donor(s) of the catalyst system(s). Therefore, the selection of a suitable stereoregulating external electron donor is also a very important part of the invention. Usually, the organometal compounds of the invention are selected among the conventional less and more halogenated cocatalysts used in the art. Consequently, the stereoregulating external electron donor(s) is(are) also usually selected among the corresponding conventional electron donors of the art.
The stereoregulating external donor(s) is(are) preferably selected from hydrocarboxy silane compounds and hydrocarboxy alkane compounds. More preferably, the stereoregulating external donor is selected from hydrocarbyloxy silane compounds which have the formula (3)
Rxe2x80x3nxe2x80x3Si(ORxe2x80x2xe2x80x3)4xe2x88x92nxe2x80x3xe2x80x83xe2x80x83(3)
wherein Rxe2x80x3 and Rxe2x80x2xe2x80x3 are, independently, a C1-C12-hydrocarbyl, and nxe2x80x3 is an integer 1-3.
More specific examples of useful hydrocarboxy silane compounds are tricyclopentylmethoxy silane, tricyclopentylethoxy silane, triphenylmethoxy silane, triphenylethoxy silane, diphenyldimethoxy silane, diphenyldiethoxy silane, dicyclopentyldimethoxy silane, dicyclopentyldiethoxy silane, methylphenyldimethoxy silane, methylphenyldiethoxy silane, ethylphenyldimethoxy silane, ethylphenyldiethoxy silane, cyclopentyltrimethoxy silane, phenyltrimethoxy silane, cyclopentyltriethoxy silane and phenyltriethoxy silane.
Still more preferably, the hydrocarbyloxy silane compound having the formula (3) is a di-(xcex1 or xcex2)-branched C4-C12-hydrocarbyl-di-C1-C3-alkoxy silane or a mono-(xcex1 or xcex2)-branched C4-C12-hydrocarbyl-C1-C3-trialkoxy silane, and most preferably it is dicyclopentyl dimethoxy silane or cyclohexyl methyl dimethoxy silane.
Assumingly, the second organometal compound interfers with the donor equilibrium by coordinating more strongly with the stereoregulating electron donor. See above. As a consequence, atactic polymerization is facilitated. Although even small amounts of the second organometal compound will shift the equilibrium in the direction of producing more high XS material, it is important to establish the amount of used second organometal compound with respect to the amount of used donor. When using an organoaluninium compound as the second organometal compound, the amounts thereof expressed as aluminium Al2 and of the stereoregulating external electron donor D preferably are such that the molar feed ratio Al2/D is from about 0.1 to about 30, more preferably from about 0.5 to about 10.
When aiming at a controlled higher amount of high XS polymer fraction, the amount of the second organometal compound must be functional, but not so high as to remove essentially all of the stereoregulating electron donor, because then, isotactic polymer is not produced in the first place. In that case, when using an organoaluminium compound as the second organometal compound, the optimal feed ratio Al2/D is from about 0.5 to about 1.5, preferably from about 0.6 to about 1.4. If the polymerization is carried out in a loop-loop reactor system, then, in order to balance the XS values in different reactors, more donor has to be added to the second loop reactor.
The amounts of the other reagents and/or components are defined more closely below in connection with the transition metal compound used in the claimed process.
As was stated above, the invention relates to a process for the preparation of an xcex1-olefin polymer product having controlled stereoregularity, comprising the successive steps of: (i) producing a first polymerization product by contacting under polymerization conditions an xcex1-olefin with a polymerization catalyst system to give a first polymerization reaction mixture; and (ii) producing a second polymerization product by contacting an xcex1-olefin with said high activity polymerization catalyst system.
According to one embodiment of the invention, the first polymerization product is produced by contacting said xcex1-olefin monomer, preferably propene and another xcex1-olefin or, preferably ethene as comonomer. The preferred propene monomer and ethene comonomer improve the properties of some propene polymer grades. Then, usually more than or equal to 90% by weight of propene is used as the xcex1-olefin monomer and less than or equal to 10% by weight of ethene is used as the comonomer. It shoud be noted that the ethene as comonomer is used in considerably larger amounts than the ethene which according to the invention is able to regulate the XS of step (ii). Compare e.g. with EP 339 804.
In the field of Ziegler-Natta catalysis, the use of an organometal compound is fundamental. The compound is generally called a cocatalyst. The use of a stereoregulating electron donor is also common. It is generally called an external electron donor. The present invention is according to one embodiment based on the interaction between the external donor and two different organometal compounds. Thus, the type of the third catalyst component mentioned, namely the transition metal component, is not critical, as long as it is capable of high activity polymerization. See the initial discussion on the meaning and role of the components.
In the claimed process, a highly active and stereospecific catalyst systems is preferred. Advantageously, the high activity polymerization catalyst system is the reaction product of a supported intermediate containing magnesium, titanium, halogen and optionally an internal donor, with the first organometal compound and the stereoregulating external electron donor. Said reaction product is preferably obtained by contacting magnesium chloride or a complex thereof, titanium tetrachloride and an internal electron donor into a solid intermediate and contacting the solid intermediate with the first organometal compound and the stereoregulating external electron donor.
In order to act as support for the titanium tetrachloride and the internal electron donor in the solid intermediate, the magnesium chloride must be in a chemically active form. This means that the magnesium chloride must have lower crystallinity and higher specific surface area than conventional commercial magnesium chloride.
Magnesium chloride may be activated mechanically. In such a process, it is dry-comilled together with the internal electron donor. Then, the comilled product is heat-treated with an excess of titanium tetrachloride, followed by repeated washings with titanium tetrachloride and/or hydrocarbons to give the solid intermediate. Typically, such a solid intermediate exhibits a high specific surface area (50-300 m2/g) and contain from 0.5 to 3% by weight of titanium.
Preferably, the magnesium chloride is activated chemically. This can be accomplished by contacting a complex of magnesium chloride, the titanium tetrachloride and the internal electron donor, whereby the complex is converted to activated magnesium chloride supporting the titanium tetrachloride and the internal electron donor.
According to one preferred embodiment of the invention, said complex of magnesium chloride is a solid adduct of magnesium chloride and an alcohol having the formula (4)
MgCl2.nRxe2x80x3xe2x80x3OHxe2x80x83xe2x80x83(4)
wherein n is 1-6, preferably 2-4 and Rxe2x80x3xe2x80x3 is a C1-C10 alkyl, preferably a C1-C3 alkyl. n is preferably 2-4. Most preferably, the solid adduct of magnesium chloride and an alcohol having the formula (4) is a complex of the formula MgCl2.3C2H5OH.
The solid adduct of magnesium chloride and alcohol having the formula (4) is conveniently prepared by heating and melting the magnesium chloride and the alcohol together, dispersing or spraying the melt into small droplets and solidifying the droplets by contact with a cooled medium. The dispersion of the melt into small droplets may typically take place by pouring the melt into hot silicon oil under stirring, thereby forming a hot dispersion of molten droplets in silicon oil. Then, the solidification is brought about by pouring the hot dispersion into cold hydrocarbon.
Alternatively the melt of magnesium chloride and alcohol is sprayed by means of pressurized inert gas through a die into a space containing cold inert gas, whereby the small droplets are formed and solidified almost instantly. This process is also called spray crystallization.
Finally, said solid magnesium dichloride/alcohol adduct which has been obtained in powder form is contacted with the titanium tetrachloride and the internal electron donor. The titanium tetrachloride both removes the alcohol thereby exposing coordination sites on the magnesium chloride and coordinates to part of the formed coordination sites. The internal electron donor coordinates to another part of the coordination sites. There may be chemical reactions between the alcohol and the internal electron donor. Anyway, the result is a solid intermediate comprising magnesium chloride supporting the titanium tetrachloride and the internal electron donor or its reaction product.
The internal electron donor used for preparing the solid intermediate is any organic compound which contains an electron donating atom such as N, P, O and S, gives catalytic activity and enables stereospecific polymerization. The art of Ziegler-Natta catalysis knows a multitude of suitable electron donors for this purpose. Preferably, the internal electron donor is a C1-C14 alkyl ester of a carboxylic acid. Typical such esters are C1-C14 alkyl esters of aliphatic dicarboxylic acids such as maleic acid, malonic acid and cyclohexanedicarboxylic acid, C1-C14 alkyl esters of aromatic monocarboxylic acids such as substituted and unsubstituted benzoic acids, and C1-C14 alkyl esters of aromatic dicarboxylic acids, such as phthalic acid.
According to a preferred embodiment of the invention, the internal electron donor is a C4-C14 alkyl ester of an aromatic carboxylic acid. More preferably, the internal electron donor is a di-C4-C14 alkyl ester of a dicarboxylic acid. Most preferably, the internal electron donor is a di-C4-C14 alkyl ester of an aromatic dicarboxylic acid, such as a di-C4-C14 alkyl phthalate.
Preferably, the above mentioned solid intermediate is produced by contacting said solid adduct of magnesium dichloride and a C1-C3 alcohol as the magnesium chloride complex and a C4-C14 alkyl ester of a carboxylic acid as the internal electron donor, whereby said complex, said titanium tetrachloride and said ester most preferably are being contacted at an elevated temperature to produce said solid intermediate in the form of a transesterification product. Thereby, said adduct, said titanium tetrachloride and said ester are contacted at 110-200 xc2x0 C., preferably at 120-150xc2x0 C. at which temperature the transesterification takes place.
When preparing the above mentioned solid intermediate, the used amounts of magnesium chloride or a complex thereof and titanium tetrachloride are such that in said catalyst system, the molar ratio Mg/Ti is preferably between about 1 and about 200, most preferably between about 5 and about 50. The used amount of said internal donor (ID) is preferably such that in said intermediate, the molar ratio ID/Ti is between about 0.1 and about 10, most preferably between about 0.3 and about 3.
When the solid intermediate is contacted with the first organometal compound and the stereoregulating external electron donor give said high activity polymerization catalyst system, the contacting can take place in one, two or more steps. According to one embodiment of the invention, said solid intermediate is preactivated first with one out of two portions containing the first organoaluminium compound, and then contacted with the other. In the preactivation the Al/Ti ratio is preferably between 0.1 and 10, more preferably between 1 and 5, most preferably between 2 and 3. Usually, the stereoregulating external donor and the first organoaluninium compound are contacted in the form of a C5-C8 hydrocarbon solution.
As is common with polymerization catalyst systems of this kind, the active catalyst system precursor can alternatively be coated with a small amount of polymer before using it in the actual polymerization. This is called prepolymerization. In a prepolymerization, said solid intermediate is typically contacted with the stereoregulating external donor and the first organoaluminium compound, as well as a small portion of an olefin (not necessary the same one as is used in the actual polymerization), under polymerization conditions, in order to obtain particles of said first high activity polymerization catalyst system which are coated with polyolefin. Such a prepolymerized catalyst system is easy to handle and has a desirable morphology.
In the high activity polymerization catalyst system used in the claimed process, the used amounts of the first organoaluminium compound expressed as aluminium Al1 and said titanium tetrachloride of said solid intermediate, expressed as titanium Ti, are preferably such that the molar feed ratio Al1/Ti leading to the high activity polymerization catalyst system is from about 1 to about 1000, more preferably from about 50 to about 500, most preferably from about 100 to about 300.
Correspondingly, the used amounts of the first organoaluminium compound expressed as aluminium Al1 and the stereoregulating external electron donor D are preferably such that the atom to mol feed ratio Al1/D leading to the first high activity polymerization catalyst system is from about 10 to about 200, most preferably from about 30 to about 100. The used amounts of the stereoregulating external electron donor D and said titanium tetrachloride expressed as titanium Ti are preferably such that the molar feed ratio D/Ti leading to the first high activity polymerization catalyst system is from about 1 to about 20, most preferably from about 2 to about 10.
The invention also covers embodiments outside the examples. Equipped with the basic information provided by this document, the parameters, reactants, etc. can be optimized to produce polyolefin having a restricted and/or controlled XS value. Thus, (i) the first polymerization product is preferably produced under conditions which give polypropene having an isotacticity, expressed as XS (xylene soluble fraction), selected from XS values lower than or equal to 8.0% by weight and higher than or equal to 1.5% by weight, more preferably XS values smaller than or equal to 5.0% by weight and larger than or equal to 2.0% by weight.
The steps or measures of the process can be carried out in any convenient apparatus, having one or more reactors. The process can be a batch or continuous process. Preferably, the process is carried out in two or more reactors comprising bulk reactors, e.g. loop reactors, preferably two or more loop reactors or one or more bulk reactors plus one or more gas phase reactors.
According to one embodiment of the invention, the first polymerization product is (i) produced in a bulk reactor, preferably in a loop reactor. Most preferably it is produced under polymerization conditions selected from:
temperature selected from temperatures which are higher than or equal to 40xc2x0 C. and lower than or equal to 120xc2x0 C., preferably temperatures which are higher than or equal to 60xc2x0 C. and lower than or equal to 100xc2x0 C.,
a pressure selected from pressures which are higher than or equal to 20 bar and lower than or equal to 80 bar, preferably pressures which are higher than or equal to 30 bar and lower than or equal to 60 bar,
a hydrogen addition for controlling the molar mass in a manner known per se.
The process according to the invention comprises the production of a second polymerization product. See step (ii) above. The second polymerization product is preferably produced by contacting propene as said xcex1-olefin monomer.
The second polymerization product is preferably produced in a gas phase reactor (GPR). Advantageously, the gas phase polymerization conditions are selected from:
a temperature selected from temperatures which are higher than or equal to 50xc2x0 C. and lower than or equal to 130xc2x0 C., preferably temperatures which are higher than or equal to 70xc2x0 C. and lower than or equal to 100xc2x0 C.,
a pressure selected from pressures which are higher than or equal to 10 bar and lower than or equal to 60 bar, preferably pressures which are higher than or equal to 20 bar and lower than or equal to 40 bar,
a hydrogen addition for controlling the molar mass in a manner known per se.
The product of the claimed process is an integrated mixture of said first polymerization product and said second polymerization product. They are integrated by (ii) producing the second polymerization product in the presence of (i) the first polymerization product. By first polymerization product is e.g. meant the whole reaction mixture resulting from the first polymerization or just a part thereof including the produced polymer. Preferably, the second polymerization is carried out in the presence of both the first polymer and its catalyst system, i.e. said polymerization catalyst system.
Advantageously, said second organometal compound is added to the polymerization catalyst system before (ii) producing the second polymerization product, preferably between (i) producing the first polymerization product and (ii) producing the second polymerization product. This is easily accomplished e.g. by adding the second organometal compound to the second polymerization reactor or preferably to the pipeline connecting the first and the second polymerization reactors, such as the loop and gas phase reactors, respectively. The small amount of olefin, preferably ethene, can be added to the pipeline or to the second reactor. Preferably it is added separately to the second reactor.
Further, the process can be preferably carried out under polymerization conditions which produce (i) first polymerization product and (ii) second polymerization product in a mass ratio selected from ratios higher than or equal to 20:80 and lower than or equal to 70:30, preferably from ratios higher than or equal to 30:70 and lower than or equal to 60:40, most preferably from ratios higher than or equal to 35:65 and lower than or equal to 65:35.
Preferably, the process of the invention is carried out under conditions which give a propene polymer product having an isotacticity, expressed as XS (xylene soluble fraction), selected from XS values lower than or equal to 8% by weight, more preferably lower than or equal to 6% by weight, most preferably lower than or equal to 5% by weight. Preferably, the XS values are higher than or equal to 1.5% by weight, most preferably, higher than or equal to 2.0% by weight.
The following advantages were reached when a small amount of ethene or other stereoregularity controlling agent were used for isotacticity control:
The feed of a donor complexing agent like EADC gives very good hydrogen sensitivity for the catalyst.
A small ethene feed to step (ii) gives better activity for the catalyst.
The morphology of the polymer was clearly better when the donor complexing agent EADC and a small amount of ethene were present in step (ii).
The same donor (dicyclopentyldimethoxy silane) can be used for very high isotacticity moulding grades as well as for film and fiber grades. The transition time when switching the reaction system from grade to grade in commercial scale will be lower and the process will be more economical. In conventional systems one donor (cyclohexylmethyldimethoxy silane) is used for film and fiber grades and another donor (dicyclopentyldimethoxy silane) for moulding grades.
The control of isotacticity is very easy by ethene and/or EADC feed from the process""s point of view. Constant donor feed can be used (Al/Ti=250 and Al/D=20) and the final control of the isotacticity is done by ethene feed and/or by using EADC or DEAC.
Lower XS values are required for film grades and then a small amount of ethene or a chlorinated organometal compound is used for balancing the isotacticities.
The application test shows that the best fiber grades are made by using the novel system.